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%I #5 Mar 04 2021 20:55:45
%S 1,1,5,23,155,1355,14371,183911,2781283,48726355,976903875,
%T 22183097191,565060532965,16016170519017,501714014484813,
%U 17265124180702953,649178961366102597,26544344366333824055,1175291769917975444817,56133021061270139242637,2881893164859601701738005
%N a(0) = 1; a(n) = Sum_{k=1..n} binomial(n,k)^2 * a(k-1).
%t a[0] = 1; a[n_] := a[n] = Sum[Binomial[n, k]^2 a[k - 1], {k, 1, n}]; Table[a[n], {n, 0, 20}]
%Y Cf. A023998, A040027, A101514, A102221, A342197, A342198, A342199.
%K nonn
%O 0,3
%A _Ilya Gutkovskiy_, Mar 04 2021
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